This invention relates to a code wheel for use with a reflective type optical rotary encoder.
Reflective type optical rotary encoders are already known wherein information of a rotating body such as a rotational frequency and a direction of rotation is determined from a beam of light which is irradiated upon and reflected from reflective portions and non-reflective portions provided on a code wheel. An example of such a code wheel will be described below with reference to FIGS. 4 and 5.
FIG. 4 is a perspective view showing general construction of a rotary encoder, and FIG. 5 is a plan view of a code wheel. Referring to FIGS. 4 and 5, a code wheel 2 in the form of a disk is mounted on a shaft 1a of a motor 1. The code wheel 2 has a plurality sectoral reflective portions 3 arranged radially in a circumferentially equidistantly spaced relationship on a flat face 2a thereof, and a plurality of of non-reflective portions 4 each located between adjacent ones of the reflective portions 3. A light emitting element 5 and a pair of light receiving elements 6 and 7 located on opposite sides of the light emitting element 5 are disposed in an optically aligned relationship to the flat face 2a of the code wheel 2 by way of optical fibers 8, 9 and 10, respectively. Thus, as the code wheel 2 rotates, a beam of light from the light emitting element 5 is reflected from the reflective portions 3 and received by the pair of light receiving elements 6 and 7 as a pair of series of pulse signals from which a rotational frequency and a direction of rotation of the code wheel 2 can be determined as well known in the art.
As seen from FIG. 5, the code wheel 2 is composed of a disk member made of a metal material such as aluminum on a surface of which the radial, equidistantly spaced, sectoral non-reflective portions 4 are formed by printing using ink of a resin material which contains therein a black, light absorbing substance such as carbon black. Meanwhile, the reflective portions 3 of the code wheel 2 are formed by exposed portions of a surface of the disk member itself of a metal material which has been treated to increase the light reflectivity and provide an anticorrosive feature.
However, such a process of producing the conventional code wheel 2 as described above has a drawback that the production cost is high because the non-reflective portions 4 are formed using a printing technique. Besides, it is another drawback of the process that the light absorbing efficiency decreases as the flatness of the black printed faces of resin ink increases.